1. Field of the Invention
The present invention relates to a line converter for coupling between dielectric lines of different kinds, and a directional coupler, dielectric line unit, high-frequency circuit module, and transmitter-receiver which use the line converter.
2. Description of the Related Art
In the high-frequency field, two types of directional couplers have been used. One type utilizes dielectric wave guides (xe2x80x9cDWGxe2x80x9d). Couplers using DWG are operable for use in broadband applications. On the other hand, DWG-type couplers are not advantageous from the standpoint of miniaturization.
A DWG directional coupler is shown in Kawai et al., xe2x80x9cA Design of Waveguide-Type Directional Couplers Based on E-Plane Planar Circuit Approach,xe2x80x9d IEICE Technical Report MW 96-22 (May 1996). The coupler is formed by dielectric waveguides (DWG) which are formed by filling dielectric material in a waveguide.
The other type of directional coupler utilizes the nonradiative dielectric (xe2x80x9cNRDxe2x80x9d) waveguide. The NRD waveguide has a disadvantage, in that the characteristic values such as power distribution ratio, and so on, can be kept within fixed limits only within a narrow bandwidth.
An example of an NRD directional coupler is disclosed in FIG. 2 of Japanese Laid-Open No. H07-283634 (equivalent to U.S. Ser. No. 08/837,836). A directional coupler 25 consists of two opposing dielectric strips 30a, 30b which are disposed on a conductor plate 5. The strips 30a, 30b are overlaid by an opposing conductor plate, not shown.
It has been proposed to combine the DWG and NRD waveguides in order to enjoy the advantages of both.
One example of such a hybrid is shown in FIG. 13 of Japanese Laid-Open No. H08-70209 (Application No. H06205426 filed Aug. 30, 1994), which corresponds to U.S. Pat. No. 5,600,289. In FIG. 13, xcex2 indicates a section formed by a DWG, while xcex3 indicates a section formed by an NRD guide. As understood from the drawing, the tapered structures are provided in order to realize a conversion from one type of line to the other.
When implementing such a hybrid structure in a directional coupler, several tapered portions may be necessary because the two opposing lines each require respective line conversions. For example, ports 1-4 of the DWG directional coupler in Kawai et al. may be connected to respective NRD guides by respective line converters. This significantly increases the size of the directional coupler.
The above-described types of line converter for coupling between the DWG and the NRD guide have the advantage of low line conversion loss over a broad band. However, the line converter becomes large-sized as a whole because of the required length of the line conversion portion.
For example, NRD guides can be used as input-output portions in a DWG-type parallel-line directional coupler in which two dielectric striplines are arranged in parallel between two upper and lower conductor surfaces. By use of the DWG waveguide type, broad-band characteristics can be obtained. However, a line converter is required between the DWG and the NRD guide. As a result, the whole system becomes large-sized.
In response to the foregoing problems of the prior art, the present invention is able to provide a small line-conversion structure between a DWG and an NRD guide.
A dielectric line converter according to the present invention has a good line conversion characteristic and is small in size.
Further, a directional coupler according to the present invention has wide-band characteristics and is made up of small-sized dielectric lines.
Further, a high-frequency circuit module and/or a transmitter-receiver according to the invention can include a dielectric line unit or a directional coupler comprising the above dielectric line converter.
According to an aspect of the present invention, a line converter comprises a first-kind dielectric line having upper and lower conductor surfaces contacting the top and bottom of a dielectric stripline and spaces beside the dielectric stripline, between the dielectric stripline and side conductive surfaces spaced away from said dielectric stripline, a second-kind dielectric line having upper, lower and side conductor surfaces substantially contacting the top, bottom and sides of a dielectric stripline, and an intermediate dielectric stripline connected between the dielectric striplines of the first-kind and second-kind dielectric lines (advantageously being continuous with the dielectric striplines of the first-kind and second-kind dielectric lines), wherein the space between the upper and lower conductor surfaces in the region of the intermediate dielectric stripline is made narrower than the space between the upper and lower conductor surfaces in the first-kind line, and wherein the space between the upper and lower conductor surfaces in the second-kind dielectric line is substantially zero.
Because of this construction, as the space between the upper and lower conductor surfaces in the region of the intermediate dielectric stripline does not change abruptly between the first-kind dielectric line to the second-kind dielectric line (which may preferably be dielectric-loaded waveguide), a line conversion takes place without deteriorating reflection characteristics, and as the line does not need to be widened, it becomes easy to make the line converter small.
In the above construction, when the space between the upper and lower conductor surfaces in the region of the intermediate dielectric line narrows gradually from the first-kind dielectric line to the second-kind dielectric line, the reflection at the discontinuity portion is further suppressed.
Further, when the length of the intermediate dielectric line between the first-kind dielectric line and the second-kind dielectric line is made an odd multiple of a quarter-wavelength of the signal on the line, the waves reflected at the two locations where in which the space changes, between the upper and lower conductor surfaces in the region of the intermediate dielectric stripline, i.e., at the respective junctions with the first-kind and second-kind dielectric lines, are superposed in opposite phase, and consequently the reflected waves are canceled. Accordingly, the reflection characteristic is improved.
Further, according to another aspect of the present invention, a line converter comprises a first-kind dielectric line having upper and lower conductor surfaces contacting the top and bottom of a dielectric stripline and spaces beside the dielectric stripline, between the dielectric stripline and side conductive surfaces spaced away from said dielectric stripline, a second-kind dielectric line having upper, lower and side conductor surfaces substantially contacting the top, bottom and sides of a dielectric stripline, and an intermediate dielectric stripline connected between the dielectric striplines of the first-kind and second-kind dielectric lines (advantageously being continuous with the dielectric striplines of the first-kind and second-kind dielectric lines), wherein the space from the intermediate dielectric stripline to the side conductor surface is made a constant value which is narrower than the space from the dielectric stripline of the first-kind dielectric line to the side conductor surface of the first-kind dielectric line.
Because of this construction, as the space between the side conductor surfaces and the intermediate dielectric stripline changes in a stepped way from the first-kind dielectric line to the second-kind dielectric line (which preferably may be a dielectric-loaded waveguide), the line converter does not have to be long. As the result, a short line converter can be obtained.
In the above construction, when the length between the first-kind dielectric line and the second-kind dielectric line is made an odd multiple of a fourth of a wavelength of the signal on the line, the waves reflected at the two locations where the space between the side conductor surfaces spaced away from the intermediate dielectric stripline changes, i.e., at the respective junctions with the first-kind and second-kind dielectric lines, are superposed in opposite phase, and consequently the reflected waves are canceled. Accordingly, the reflection characteristic is improved.
The first-kind dielectric line in any of the above aspects of the invention advantageously can be a hyper-NRG guide, which propagates only the LSM mode, by making the space between the upper and lower conductor surfaces of the first-kind dielectric line narrower than the height of the dielectric stripline of the first-kind dielectric line. Thus, a dielectric line circuit having a dielectric line and dielectric-loaded waveguide in which there is hardly any mode conversion loss at a bend in the dielectric line can be easily constructed.
According to another aspect of the present invention, one of the above dielectric line converters can be modified to provide a dielectric line unit. For example, a circuit board and a microstripline on the circuit board can be disposed within a second-kind dielectric line, and one of the above dielectric line converters can be connected to said second-type dielectric line. Thus, a dielectric line unit including the second-kind dielectric line can be constructed so that a first-kind dielectric line can be directly connected to the dielectric line unit.
According to a further aspect of the present invention, the above dielectric line converters can be employed in a directional coupler. For example, two second-kind dielectric lines of two respective line converters can be joined together or integrated at a coupling region to constitute a directional coupler. In this way, a directional coupler into which signals can be input through an NRD guide and which has a broad-band characteristic can be obtained.
Further, according to other aspects of the present invention, the above dielectric line units or directional couplers can be used to propagate a transmission signal or a reception signal in a high-frequency circuit module.
Furthermore, also according to aspects of the present invention, a transceiver can be provided by one of the above high-frequency circuit modules, together with a transmission circuit and a reception circuit.
Other features and advantages of the invention will be understood from the following detailed description, together with the drawings, in which like references denote like elements and parts.